Blade for excavating mechanism



Jan. 24, 1956 G. A. JOHANSSON 2,731,742

BLADE FOR EXCAVATING MECHANISM Filed Feb. 2, 1953 INVENTOR. G (A JJVmwmz United States Patent C 2,731,742 BLADE FOR EXCAVATING MECHANISMGustaf A. Johansson, Chicago, Ill., assignor to The United Electric CoalCompanies, Chicago, 11]., a corporation of Delaware Application February2, 1953, Serial No. 334,647 11 Claims. (Cl. 37-189) The presentinvention relates to excavating apparatus and to cutting blades fordigging wheels of excavating apparatus. In particular, the inventionrelates to a cutting blade for excavating apparatus of the typedisclosed in the copending application of Frank F. Kolbe, Serial No.281,950, filed April 12, 1952.

In the identified copending application, there is disclosed anexcavating apparatus comprising a pair of spaced rotary digging wheelsadapted to be moved against a bank of earth material for cuttingmaterial from the bank, the cut material being retained by the wheelsand directed thereby to a discharge conveyor. In use of the apparatus,the digging wheels, comprising wheel hubs with blades mounted thereon,are moved laterally of the bank of material so that the blades cutsideways into the bank. To guide the cut material into the space betweenthe wheels and to force the material between the wheels onto theconveyor, the blades must present inclined surfaces adapted to performthe stated functions. In the copending application, the cutting bladesare shown in one form as comprising flat, sheet-like blades mounted onthe wheel hubs and inclined with respect to the path of rotation of thewheel to cut the material equally well when swinging arcuately in eitherdirection.

The primary object of the present invention is to provide an improvedcutting blade for digging wheels of excavating apparatus of thecharacter described.

Another object of the invention is to provide a cutting blade for dig gwheels of the character shown in the identified copending applicationadapted to be positioned on a hub to present an etficient and effectivecutting edge and an inclined surface leading from the cutting edge tothe inside of the wheel adapted to perform the material guiding andimpelling functions stated hereinbefore.

A further object of the invention is to provide a digging wheel bladehaving a cutting edge inclined from the bottom to the top thereof in thedirection of rotation of the wheel so that the blade performs aprogressive cut on materials engaged thereby.

Another object is to provide a digging wheel blade having a cutting edgecurved rearwardly and upwardly from the bottom to the top in thedirection of rotation of the wheel with the curvature being such thatthe resisting force of the bank being cut preferably will have itsnormal component forward of a rear heel, or shear lug so as to reducethe bending moment of the normal force acting on the blade when cutting.

A still further object is to provide a digging wheel cutting bladeincluding simple means for removably securing the blade to a diggi gwheel hub.

Additional objects include the provision of an economical long wearingcutting blade adapted for strenuous service and further adapted to quickand convenient replacement should same become damaged due toencountering boulders, rock layers and the like.

Other objects and advantages of the present invention will becomeapparent in the following detailed description of a preferred embodimentof the invention, wherein Patented Jan. 24, 1956 2 reference is made tothe accompanying drawings, in which:

Figure 1 is a plan view of one form of excavating apparatus with whichthe blade of the present invention is adapted for use;

Figure 2 is a plan view of the cutting blade of the present inventionmounted on the hub of a digging wheel, the hub being shownfragmentarily;

Figure 3 is a side elevation of the cutting blade mounted on the wheelhub, the hub and mounting means for the cutting blade being shown incross section; and

Figure 4 is a cross sectional view taken substantially on line 4-4 ofFigure 3.

Referring now to the drawings, and particularly to Figure 1, theexcavating apparatus with which the cutting blade of the presentinvention is adapted for use is shown as comprising a gear housing 10adapted to enclose a drive shaft 12 and a worm gear 14 secured to thedrive shaft 12 and meshing with a pinion 16 secured to a wheel shaft oraxle 18. Digging wheels 20 are secured to the outer ends of the shaft-oraxle 18 and are provided, on their peripheral surfaces, with a pluralityof blades 22, the blades being shown somewhat schematically in Figure 1.A conveyor belt 24 extends rearwardly from the digging wheels 20 and isadapted to lead to a point of material discharge, the conveyor beltbeing driven in a conventional manner and being mounted for rotation ona terminal roller 25, having its axle suitably journaled in the frame 26of the excavating apparatus. A guide plate, not shown, extends from aposition between the digging wheels 20, beneath the housing 10, intooverlying relationship with respect to the conveyor belt 24 to guideearth materials from the space between the digging wheels 20 onto theupper run of the conveyor belt 24.

In operation, the excavating apparatus is adapted to be swunghorizontally, as indicated by arrow A, to move the cutting blades 22 ofone digging wheel 20 into engagement with a bank of material to remove alayer of material from the bank, as is shown in Figure 1. As the blades22 are moved into engagement with the bank of material, the cuttingedges thereof bite into the bank and remove material therefrom, thematerial being guided upon continued rotation of the digging wheels 20into the space between the digging wheels by the forwardly disposedinclined surfaces of the cutting blades. The inclined surfaces of thecutting blades 22 effecting the cut move the material into the spacebetween the wheels and the inclined surfaces of the cutting blades 22 ofthe other digding wheel 20 prevent discharge of earth materials from thespace between the wheels laterally thereof. The bank of material closesthe forward end of the space between the wheels so that the inclinedsurfaces of the blades, ongaging the material between the Wheels, forcethe material in the direction of rotation of the wheels to move sameonto and over the surface of the guide plate, the guide plate serving todirect the material from the space between the wheels onto the conveyorbelt 24 which carries the material to a point of disposal.

From the foregoing, it will be appreciated that the cut ting blades forexcavating apparatus of the general type described must present acutting surface or edge to cut into the bank of material and mustpresent inwardly directed and forwardly disposed inclined surfaces toguide and propel the material into the space between the wheels and toretain the material in that space until the cut material passes from thecut bank and traverses the guide plate whence it is discharged in agenerally tangential direction and lands on the top of the conveyor belt24. The present invention is directed to the provision of a cuttingblade having :these predominant characteristics.

Referring now to Figures 2 :to 4, the cutting blade 22 of the presentinvention is shown as comprising a cast metal body 30, which may becored, if desired, to provide a hollow portion 31 intersected by aplurality of re-cnforcing ribs 32. The body 39 is provided with a widebase portion 34 and the bladetapers upwardly and forwardly with respectto the base portion 34 to provide an inclined inner surface 36. Theblade is adapted to be mounted on a wheel hub adjacent the edge thereof.so that the inclined surface 36 extends diagonally of the hub and leadsfrom adjacent the outer edge of the wheel inwardly toward the inside ofthe wheel. As previously stated, the body tapers upwardly and forwardlyto provide a terminal inclined edge 38 constituting the cutting edge ofthe blade. The cutting edge 38 is preferably curved in form, as shown inFigure 3, so as to provide the most effective cutting edge possible. Asshown in Figure 3, the cutting edge 38 is preferably inclined rearwardiyand upwardly from the forward edge (the left-hand edge in Fig. 3) towardthe trailing edge in the direction of rotation of the digging wheel soas to present a cutting edge adapted to eifect a progressive cut on thebank of material to be engaged by the blade. It will be observed thatthe curvature of cutting edge 38 is generally arcuate and changes itscurvature, as at 38a, to an arc of shorter radius.

The curvature of the cutting edge 38 is such that the resistant force ofthe excavated material against it has its normal component acting in aline intersecting the base of the blade between its front and rear, andpreferably intersecting the base ahead of the heel or shear lug 60 whichlug will be described hereinafter.

It will be observed that the base portion 34 of the blade 22 generallyis wide relative to the cutting edge 38. The base portion also widensfrom its forward portion, where the cutting edge 38 comes down to meetit, towards its rear portion, where it abuts the heel, or shear lug 60.Consequently, the blade is enabled better to resist being bent sidewaysby such component of force as is exerted sideways against the inclinedsurface 36 as the bank is cut into. It will be observed that as thecurved cutting edge rotates more deeply into the bank, and thereforemeets increasing resistance, the resultant component of lateral forceagainst the inclined surface 36 moves rearwardly where the base 34becomes wider and can, therefore, better resist lateral bending.

To prevent accumulation of materials within the cored portion of thecutting blade and to prevent occurrence of resistance to cutting due toaccumulation of material within the cored section of the blade, thecored side of the blade may be suitably covered by a plate 40 which maybe secured in any desired manner, preferably by welding, to the surfacesof the cored side of the blade. The cored out portion of the blade isvery important as the means of reducing dead weight which by its inertiawhen rotating will add too much of a shock load to the wheel whenboulders and rocks are encountered.

In use, the cutting blade performs the functions described hereinbeforewith respect to the operation of the excavating apparatus shown inFigure 1. in other words, as the digging wheels are rotated in thedirection indicated by the arrow B in Figure 3, the cutting edge 38 willcut into the bank of material with which engaged to remove or cut away aportion of the material. As the cutting edge 38 bites into the material,the material will engage the inclined inner surface 36 of the blade andwill be directed thereby to the inside of the wheel and into the spacebetween the two digging wheels 20. In addition, the inclined surface 36of the cutting blades will force the material within the space betweenthe Wheels in the direction of travel of the wheels and onto and overthe guide plate to the conveyor, as described, hereinbefore.

Due to the fact that the cutting blades must frequently engage rocks,boulders, and other materials having substantial resistance to cutting,it is preferable that the blades be removably mounted on the surface ofthe digging wheel hub so that individual blades may be readily removedand replaced should damage occur thereto. Ac-

cordingly, while the blade, as described hereinbefore, may be suitablysecured to the digging wheel hub merely as by welding or the like, it ispreferable that the blades be removably or detachably mounted on the hubin the following manner.

The hub 42 of digging wheel 20 is shown as being cylindrical because ofthe economy and strength of cylindrical objects. However, the diggingwheel hub 42 may be of polygonal form, as is shown in the copendingapplication of Frank P. Kolbe, or may be otherwise suitably shaped asdesired. The number of blades to be mounted on the hub may be selectedat the discretion of the designer, and at each blade location, the hub42 is provided with three spaced and laterally offset slots or apertures44. A re-enforcing plate 46 is suitably secured, as by welding, to theinner surface of the hub 42 at each slotted portion thereof to increasethe rigidity and strain resistance of the hub at that location, there-enforcing plate 46 being provided with apertures 48 aligned with theapertures 44 in the hub 42. The cutting blade 22 is preferably providedwith a plurality of lugs 50, the number of lugs corresponding to thenumber of apertures or slots in the hub 42 and re-enforcing plate 46.The lugs 50 are formed integrally with the base portion 34 and extend ina direction opposite from the body 30 of the blade 22. They are spacedfrom one another and laterally offset from one another, as indicated inFigure 2. The lower surface of the base 34 of the blade 22 is shaped tocorrespond to the surface configuration of the wheel hub, the lowersurface of the base being arcuate in form in the preferred embodiment ofthe invention. The individual cutting blades 22 are adapted to beassociated with'the wheel or hub 42 by inserting the lugs 50 through theapertures 44 and 48, and the body 30 of the cutting blade may beproperly fitted to and aligned with the surface of the hub by means ofshims 56 which may be suitably welded to the base portion 34 of theblade. The lower edge of the base portion 34 of the cutting blade isprovided at the trailing edge thereof with a notch 58 adapted for thereception of a heel or shear lug 60 suitably secured to the surface ofthe hub 42, as by welding or the like. The cutting blade is positioned.upon the digging wheel hub in such manner that the edges of the bladedefining the notch 58 engage the surfaces of the shear lug 60 in firmabutting relation.

Each of the cutting blade lugs 50 is provided withv a slot 62 adaptedfor the reception of a wedge member, indicated generally at 68. Theslots 62 in the lugs 50 are each provided with a terminal portion at thetop thereof extending parallel to the lower surface of the base 34 ofthe cutting blade and disposed outwardly of the inner, or under, surfaceof the wheel hub, and each have a lower terminal edge inclined withrespect to the upper terminal edge and disposed a substantial distanceradially inwardly of the inner surface of the hub. As will be noted fromFigure 3, the slots 62 are formed in the lugs 50 during casting of thecutting blade and, accordingly, the terminal portions of the slots arerounded and are not finished. To provide a wedging surface, a wedge orwear plate 79 is positioned in each slot 62, at the bottom thereof, andis secured in the slot preferably by welding, as indicated at 72. Thewedge or wear plate presents an upper surface inclined with respect tothe lower surface of the base 34' of the cutting blade, and is adaptedfor the reception of a wedge member 74. An adjustable shim 76 issuitably secured, as by welding, to the upper surface of the wedgemember 74. As shown in Figure 4, the wedge 74 has a fiat upper surfaceand an inclined lower surface adapted to cooperate with the inclinedsurface presented by the wedge or wear plate 70. The wedge plate 70 ispreferably associated with the lugs 50 prior to mounting of the cuttingblade on the wheel hub. the shims 76 are suitably chosen prior tomounting of the cutting blade on the wheel hub so that the assembly maybe readily and conveniently accomplished. 5

Accordingly, the individual cutting blades are separately Likewise, theshims 56 and and removably associated with the digging wheel hub and arereadily and conveniently mounted on the hub by insetting the lugs of thecutting blade through the apertures in the wheel hub and there-enforcing plate, and forcing the blade into engagement with the shearlug 60, after which the cutting blades may be secured to the diggingwheel hub by jamming each of the wedge members 74 into wedgingengagement with the respective lower surface of the re-enforcing plate46 and the upper surface of the wedge or wear plate 70. The wedge plate70 and the wedge 74 preferably provide cooperating inclined surfaces,having a slight degree of inclination so that the wedge will beautomatically locked in position and will not of itself tend to loosen.The lugs 50 are spaced from one another and are laterally offset, aspointed out hereinbefore, so that the wedge members 74 may beindividually and conveniently driven into locking relationship with thelugs and the wheel hub.

Due to the configuration of the cutting edge 38 of the blades of thepresent invention, the blades will automatically tend to retract fromany obstruction met thereby, such as boulders and rock layers, but, ifretraction of the blades is not possible, it is desirable in certaininstances to provide means accommodating the automatic disassociation ofthe blade and Wheel hub upon encountering in irresistible object so thatthe wheel hub and the driving mechanism for the digging wheels will notbe damaged.

According to the present invention, the shear lug 60 is provided toprevent rearward movement of the cutting blade with respect to thedigging wheel hub, regardless of the objects encountered by the cuttingblade. Further, according to the invention, the wedge members 74 mayconveniently constitute shear members which are adapted to shear off,upon occurrence of the blade encountering objects of substantialresistance, so that the cutting blade may pivot about the forward edgeof the shear lug 66, and if necessary, become disassociated from thedigging wheel hub to avoid damage to the digging wheel hub or to thedriving mechanism for the digging wheels. The design of shearable wedgemembers 74 may be made according to standard engineering principles.However, other instances may occur wherein it is not desirable toprovide means accommodating shearing off of the cutting blades. In thoseinstances, the cutting blade, the shear lug, the Wedge members, thewheel hub and the re-enforcing plate are designed of such dimensions andmaterials as to resist any load that may be encountered, any force inexcess of a predetermined value resulting in stoppage of the diggingwheel driving mechanism. Either design may be readily carried out inaccordance with the present invention.

As pointed out hereinbefor'e, it is desirable to have the cutting bladeof the present invention prepared completely for quick and convenientassembly on a digging wheel hub. The reason for this will be readilyapparent when the cutting blades are considered as replacements unitsfor other blades and can be utilized to replace cutting blades only whenthe excavating mechanism is stopped. To render the cutting blades of thepresent invention immediately usable as replacement blades, adapted tobe quickly secured to a wheel hub to prevent prolonged shut-down of theexcavating apparatus, the present invention contemplates the formationand the adjustment of the various elements of the cutting blade prior touse thereof, the particular adjustments being accomplished byutilization of a master jig.

The master jig may consist of a section corresponding to a section of adigging wheel hub upon which the blades are to be mounted, such as isshown in Figure 3. The blade is placed in the jig and the lower edge ofeach of the slots 62 in the lugs 5b is ground smooth and the wedge block70 is inserted therein. Thereafter, the wedge member 74 is inserted inthe slot on top of the wear plate 70 until the wedge member isapproximately centered with regard to the lug. The spacing between thetop surface of the wedge member 74 and the lower surface of the jig isthen measured to determine the necessary thickness of the shim 76. Ashim of the necessary thickness is selected and the wedge member 74 isremoved from the lug and the shim 76 is placed on top thereof andsuitably ecured thereto, with the ends of the shim turned over andextending along the sides or end surfaces of the wedge member 74. Whenthe foregoing adjustments have been made for all three lugs, the threewedge blocks or members are driven into tight position to hold the wearplate 76 in position. The wear plate is then Welded into the lug, as isindicated at 72. Thereafter, the alignment and positioning of the bladeon the jig is checked and suitable shims 56 are secured to the lowersurface of the blade to insure proper alignment thereof. The blade isthen completely adjusted and usable as a replacement unit with the threelugs being provided with separate mar rings, the individual wedgemembers for the respective lugs being provided with correspondingmarkings, and with the blade and the three wedge members thereforpreferably being stored together.

From the foregoing, it will be appreciated that the present inventionprovides a cutting blade adapted to perform an etficient cutting actionon earth materials and to direct those materials, after cutting, asrequired according to the type of excavating apparatus with which theblade is utilized, the blade being sturdy and economical of manufactureand being particularly adapted for ready and convenient assembly with anexcavating wheel hub.

While I have described what I regard to be a preferred embodiment of myinvention, it will be apparent that various changes, rearrangements andmodifications may be made therein without departing from the spirit andscope of the invention, as defined by the appended claims.

I claim:

1. A cutting blade for excavating apparatus comprising a body portionhaving a base and tapering upwardly and forwardly with respect to saidbase, lugs extending from said base in a direction opposite to said bodyportion, said lugs each having a slot therein, and wedge members adaptedto be inserted in said slots to secure the cutting blade to excavatingapparatus, said wedge members comprising a wedge block and shim meansadapted to be secured to said wedge block to vary the thickness thereof.

2. A cutting blade for excavating apparatus comprising a base, a bodyportion tapering upwardly and forwardly with respect to said base, shimsadapted to be secured to said base, lugs extending from said base in adirection opposite to said body portion, each of said lugs having a slottherein, a wedge member for each lug adapted to be received in the slotin said lug, and a wear plate secured in the slot in said lug andpresenting a wedge surface with which said wedge member is adapted tocooperate, said wedge members each comprising a wedge block and shimmeans adapted to be secured to one surface of said wedge block to varythe thickness thereof.

3. A cutting blade for excavating apparatus comprising a base, a bodyportion tapering upwardly and forwardly with respect to said base topresent a cutting edge at the periphery of said body portion, said bodyportion having a curved peripheral portion along which said cuttingedges lies, the curvature of said peripheral portion being such that aforce exerted normal to said cutting edge intersects said base, saidbody portion including an inclined side wall surface extendingrearwardly and laterally away from said cutting edge, said body portionbeing cored from the side thereof opposite said inclined surface toprovide a hollow portion to the blade, and a plate fixed to said bodyover the cored portion thereof.

4. A digging wheel for excavating apparatus comprising a wheel hub, aplurality of cutting blades detachably mounted on said hub incircumferentially spaced relation, said blades extending generallyradially from said hub,

said blades each comprising a base portion, a body portion taperingupwardly and forwardly from said base portion, said body portion havinga peripheral cutting edge curving upwardly and rearwardly with respectto the forward edge of said base portion in the direction of rotation ofsaid hub, the curvature of said cutting edge being such mat a forceexerted normal to any point on said cutting edge intersects said baseportion, and a pinrality of lugs extending from said base portion in adirection opposite said body portion, said lugs including at least onelug adjacent the leading edge of the blade and a plurality of lugsadjacent the trailing edge thereof, said wheel hub having aperturestherein adapted for the reception of each lug on each cutting blade,each of said lugs having a slot therein transversely of the respectiveblade, and a wedge member inserted in the slot in each lug transverselyof the respective blade in wedging engagement with the respective lugand with the inner surface of said hub to detachably secure said bladesto said hub.

5. A digging wheel for excavating apparatus comprising a. hollow wheelhub, a plurality of cutting blades detachably mounted on the outersurface of said hub, said blades each comprising a base portion, a bodyportion tapering upwardly and forwardly from said base portion topresent a cutting edge the perimeter of said body portion and a surfaceextending diagonally of said hub, and a plurality of lugs extending fromsaid base portion in a direction opposite said body portion, said wheelhub having apertures therein adapted for the reception of one. lug oneach cutting blade, each of said lugs being adapted to project throughthe outer surface of said hub and having a slot therein extending from apoint inwardly of the inner surface of said hub to a point outwardly ofthe inner surface of said hub, a wedge plate positioned in the slot ineach lug at the radially inward end thereof, and wedge members adaptedto be inserted in the slot in each lug in wedging action with therespective wedge plate and with the inner surface of said hub todetachably secure said blades to said hub.

6. A digging wheel for excavating apparatus compris ing a wheel hub, aplurality of cutting blades detachably mounted on said hub, each bladehaving a cutting edge curving upwardly and rearwardly in the directionof rotation of the wheel, a heel member secured to the hub and abuttingthe rear of each blade, a plurality of lugs on each blade, said wheelhub having apertures adapted for the reception of each lug, each of saidlugs having a slot therein, and wedge members adapted to be inserted inthe slot in each lug in wedging action with the respective lug and withthe inner surface of said hub to detachably secure said blades to saidhub, said wedges of each blade being less strong in shear than said heelmember whereby when a predetermined excessive resistance is met saidwedges will shear and said blade will pivot about the heel member.

7. A cutting blade for excavating apparatus comprising a body portionhaving a base adapted to be connected with a rotating digging wheel,said body portion having a cutting edge curving upwardly and rearwardlywith r-- spect to the forward edge of said base in the direction ofrotation of the wheel to afford a progressive cut, said base having anotch in the trailing edge thereof, and a shear lug adapted to beconnected with the digging wheel fitted into said notch in said base,the curvature of said cutting edge being such that a force exertednormal to any point on said cutting edge intersects said base forwardlyof said shear lug.

8. A cutting blade for excavating: apparatus cornprising a base portionof increasing width from the lead ing end to the trailing end thereof, abody portion extending generally upward from said base portion andtapering upwardly and forwardly to define a cutting edge at theperiphery thereof, said cutting edge being curved upwardly andrearwardly from the leading end of said base portion, the curvature ofsaid cutting edge being such that a force exerted normal to any point onsaid cutting edge intersects said base portion, the projection of saidcutting edge on said base portion being of a length less than that ofsaid base portion, said cutting edge commencing at the leading end ofsaid base portion and terminating in upwardly and forwardly spacedrelation to the trailing end of said base portion, said body portionpresenting a trailing edge inclined from the trailing end of saidcutting edge downwardly and rearwardly to the trailing end of said baseportion, said base portion having a rearwardly open notch therein at thejuncture of the trailing edge of said body portion and the trailing endof said base portion, and a shear block adapted to be secured to theexcavating apparatus positioned in said notch.

9. A cutting blade for excavating apparatus comprising a base portion ofincreasing width from the leading end to the trailing end thereof, abody portion extending generally upward from said base portion andtapering upwardly and forwardly to define a cutting edge at theperiphery thereof, said cutting edge being curved upwardly andrearwardly from the leading end of said base portion, the curvature ofsaid cutting edge being such that a force exerted normal to any point onsaid cutting edge intersects said base portion, the projection of saidcutting edge on said base portion being of a length less than that ofsaid base portion, said cutting edge commencing at the leading end ofsaid base portion and terminating in upwardly and forwardly spacedrelation to the trailing end of said base portion, said body portionpresenting a trailing edge inclined from the trailing end of saidcutting edge downwardly and rearwardly to the trailing end of said baseportion, at least one attaching lug extending downwardly from said baseportion adjacent the leading end thereof, and a plurality of attachinglugs extending downwardly from said base portion at the wider portionsthereof adjacent the trailing end thereof.

10. A cutting blade for excavating apparatus comprising a base portionof increasing width from the leading end to the trailing end thereof, abody portion extending generally upward from said base portion andtapering upwardly and forwardly to define a cutting edge at theperiphery thereof, said cutting edge being curved upwardly andrearwardly from the leading end of said base portion, the projection ofsaid cutting edge on said base portion being of a length longer thanthat of said base portion, said cutting edge commencing at the leadingend of said base portion and terminating in upwardly and forwardlyspaced relation to the trailing end of said base portion, said bodyportion presenting a trailing edge inclined from the trailing end ofsaid cutting edge downwardly and rearwardly to the trailing end of saidbase portion, said base portion having a rearwardly open notch thereinat the juncture of the trailing edge of said body portion and thetrailing end of said base portion, a shear block adapted to be securedto the excavating apparatus positioned in said notch, the curvature ofsaid cutting edge being such that a force exerted normal to any point onsaid cutting edge intersects said baseportion forwardly of said shearblock, at least one attaching lug extending downwardly from said baseportion adjacent the leading end thereof, a plurality of attaching lugsextending downwardly from said base portion at the wider portionsthereof adjacent the trailing end thereof, said attaching lugs eachhaving a slot therein transversely of said blade, and a wedge memberinsertable in the slot in each of said lugs, said wedge members beingless strong in shear than said shear block.

11. A digging wheel for excavating apparatus corn prising a hollow wheelhub, a plurality of cutting blades detachably secured to said hub incircumferentially spaced relation, said blades extending generallyradially outwardly of said hub, each of said blades comprising a baseportion engaging the surface of said hub of increasing width from theleading end to the trailing end thereof,

a body portion extending generally radially outwardly from said baseportion and tapering outwardly and forwardly to define a cutting edge atthe periphery thereof, said cutting edge being curved radially outwardlyand rearwardly from the leading end of said base portion, the curvatureof said cutting edge being such that a force exerted normal to any pointon said cutting edge intersects said base portion, the projection ofsaid cutting edge on said base portion being of a length less than thatof said base portion, said cutting edge commencing at the leading end ofsaid base portion and terminating in radially outwardly and forwardlyspaced relation to the trailing end of said base portion, said bodyportion presenting a trailing edge inclined from the trailing end ofsaid cutting edge inwardly and rearwardly to the trailing said baseportion adjacent the apertures therein through which each of theattaching lugs on each of said blades extend, said hub including a shearlug secured thereto adjacent the trailing end of each of said blades,said shear lugs being positioned in said notch in the respective blade,and a wedge member insertable in the slot in each of the attaching lugsof each of said blades transversely of the respective blade, said wedgemembers each wedgedly engaging the respective attaching lug and theinner surface of said hub, said wedge members of each blade being lessstrong in shear than the respective shear lug whereby when apredetermined excessive resistance is met, said wedge members will shearand said blade will pivot about said shear lug, and shim means foradjusting each of said blades on said hub and for adjusting each of saidwedge members in the respective attaching lug.

References Qited in the file of this patent UNITED STATES PATENTS 5,229Anthony Aug. 7, 1847 607,418 Bandeen July 19, 1898 779,442 Richmond etal Jan. 10, 1905 927,331 Dagel July 6, 1909 1,195,397 Reed Aug. 22, 19161,285,514 Whidden Nov. 19, 1918 1,750,202 Steeves Mar. 11, 19301,770,679 Turner July 15, 1930 2,312,371 Strandlund Mar. 2, 19432,545,173 Shaw Mar. 13, 1951 FOREIGN PATENTS 734 Great Britain 1901

